Apparatus and method for use in the treatment of hammertoe

ABSTRACT

The apparatus and method is directed to a pair of self-tapping, interconnecting, externally and internally threaded devices that, when installed between two separate pieces of material, will draw and hold the material together as a single threaded unit. While the pair of threaded devices are being fastened into the host material, due to the unique design of their threads, no radial outward forces are produced that could cause cracking or splitting of the sections of the material into which they are installed. The external threads are helically defined into the exterior of each half of the device with a right hand thread defined into one half and a left hand thread into the other half. When the two halves are being fastened together, the increased thread pitch on one of the halves continuously draws the halves into each other even when the internal threads have already been maximally tightened.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to the field of orthopedics, and more particularlyto a bone pin for the coupling of two separate pieces of bone togetherfor use in the surgical correction of hammer toe.

2. Description of the Prior Art

One surgical method of treatment of hammertoe involves the surgicalimplantation of bone pins, and more particularly, an interphalangealfusion pin which provides an anatomically correct angle between a firstphalange and a second phalange, such as the proximal phalange and theintermediate phalange which exists at the proximal interphalangealjoint, wherein the pin is comprised of a resorbable or permanentmaterial.

Digital deformities of the fingers and toes are some of the most commonconditions encountered by orthopedists and podiatrists. Patients withdigital deformities often experience significant pain from structuralabnormalities. Some of these abnormalities are acquired, caused bytraumatic injuries, neuromuscular pathologies, systemic diseases, ormechanical problems secondary to extrinsic pressures. The deformitiesare popularly known as either mallet finger, jersey finger, coach'sfinger, hammer toe, as well as a host of others indicative of severaldifferent pathologies.

Hammer toe is generally described in the medical literature as anacquired disorder, typically characterized by hyperextension of themetatarsophalangeal joint (MTPJ), hyperflexion of the proximalinterphalangeal joint (PIPJ), and hyperextension of the distalinterphalangeal joint (DIPJ). Although this condition can beconservatively managed (e.g., through the use of orthotic devices), incertain instances surgical intervention is required.

In order to prevent recurrence of the deformity and ensure the successof the surgical procedure, a proximal interphalangeal (PIP) jointarthrodesis is typically performed. The “end-to-end” or “peg-in-hole”techniques are the most commonly used procedures. The PIPJ is alignedwith the rest of the toe in a corrected anatomical position andmaintained in place by the use of a 0.045 Kirschner wire (K-wire) whichis driven across the joint. Initially, the wire is placed from the PIPJthrough the tip of the toe. It is then driven in retrograde fashion intothe proximal phalanx. The exposed wire exiting the toe is bent to anangle greater than 90 degrees, and the bent portion is cut at 1 cm fromthe bend. At the conclusion of the surgical procedure, a smallcompressive dressing is placed around the toe, with a Jones compressionsplint being used for three to four weeks to protect the pin and the toein order to maintain correction. The K-wire and the Jones splint aregenerally removed three weeks after surgery. Similar procedures may befollowed to create arthrodesis of the distal interphalangeal joint (DIP)of the toe or for arthrodesis performed in the finger to correct digitalabnormalities of the hand.

Although this type of surgical procedure has alleviated the discomfortof hammer toe and other abnormalities of the toe and finger joints forcountless patients, the use of K-wire can result in the possiblepost-surgical misalignment of the phalanges (e.g., caused by distractionof the K-wire), as well as swelling, inflammation, and possibleinfection at the site of the exposed K-wire segment.

Of recent interest in the treatment of toe deformities, such as hammertoe, are prosthetic devices which have been used to treat deformities ofthe finger joints. For example, these devices can be inserted intoadjoining phalanges of the finger and can serve to function ostensiblyas a normal knuckle would. Because it is generally necessary to permitone or more of the joints of the finger to flex and bend, some of thesedevices are slightly angled to provide for an anatomically acceptableinterphalangeal joint angle of the finger. Furthermore, some of thesedevices allow the joint portion to bend to a significant degree, thuspermitting the finger a relatively wide range of articulation.

These devices are typically comprised of metallic or thermoplasticmaterials which, while being biocompatible, are also physiologicallyinert and thus are not resorbed by the body. There are, however,conditions in which an arthrodesis, or fusing of the affected finger ortoe joint is desired, making a permanent device which is designed topermit joint flexion/extension inappropriate. Thus, the use of thesepermanent prosthetic devices in the treatment of hammer toe and otherdigital deformities, wherein the goal of the operation is arthrodesis,whereby the presence of the device would only be required for a shortnumber of weeks to aid in maintaining correct anatomical alignment ofthe phalanges for fusion, would not be indicated. Additionally, thesepermanent devices would also be contraindicated in the treatment ofcertain finger conditions where the phalanges need to be correctlyanatomically aligned for only a few weeks until a proper amount ofhealing for fusion has occurred.

BRIEF SUMMARY OF THE INVENTION

The illustrated embodiments of the disclosed apparatus and method isdirected to a pair of self-tapping, interconnecting, externally andinternally threaded cylindrical bone pin halves that when installedbetween two separate pieces of material or bone, will draw and hold thebone together as a single unit. The pin halves have an axial boredefined therethrough. One half with internal threading defined in thebore and mating external threading defined into a exterior surface of amale peg from the other half. The two halves are threaded together bymeans of mating internal threading and the external threading on themale peg. While the pair of threaded pin halves are being fastened intothe host material or bone, due to the unique design of their externalthreads no radial outward forces are produced that could cause crackingor splitting of the sections of the bone into which they are implanted.The external threads are defined into the exterior surface of each halfof the pin, one half with a right hand thread and the other half with aleft hand thread. When the two halves are joined together, the increasedthread pitch on one of the halves continuously draws bone segments intowhich the halves have been implanted into each other even when theinternal threads of each half have already been fully tightened.

The current device also comprises interlocking hook self-tapping threadswhich provide sharp and efficient cutting edges for self-tapping intothe host material. Repository spaces are present in each of the devicehalves for collecting all of the chips created in the tapping process.

Another component of the current device is the adjustable drawingcapability of the opposing halves of the device. The opposing forcecreates a clamping load that secures the bone pin immediately andpermanently into the host material or bone. The combination of theinterlocking hook threads and the opposing pressure flanks of each halfof the bone pin together form the perfect thread engagement, producing astrong and durable connection between the two halves.

The interlocking external threads of the device mechanically join withthe surrounding host material or bone segments when the two halves areassembled and tightened together. When used in bone, this interlockingfunction promotes bone regeneration for faster healing due to the uniqueload bearing capability and the ability to draw the mating ends of thebone tightly together and hold them firmly. This is the single mostimportant factor in promoting rapid bone remodeling and shortening thepost-operative recovery period.

In a simple and effective way, the disclosed thread design creates aninstant interlocking threaded union, excellent uniform axialload-bearing capability, and very good resistance to vertical shear andbending loads. The unique interlocking hook thread prevents radialoutward spreading forces from occurring when the device is tightened andor loaded. The device can also be easily removed and reinstalled ifneeded.

While the following description will describe an apparatus and methodfor inserting the current device into bone, and more specifically totreat the medical condition known commonly as hammer toe, it is to beexpressly understood that the current device may be used for any similartype of medical procedure without departing from the original spirit andscope of the invention. Similarly, it is to be expressly understood thatthe current device may be installed in other host materials such aswood, plastic, metal, or any other material now known or later devisedin order to couple two separate pieces of the said host materialtogether.

More formally, the illustrated embodiment of the invention includes anapparatus for coupling at least two pieces of host material together,such as two phlanges in a hammer toe, comprising: a hollow proximal halfwith an internal surface and an external surface for implantation intoone of the two pieces of the host material; a hollow distal half with aninternal surface and an external surface for implantation into the otherone of the two pieces of host material; and threading for threadablyengaging the distal half and proximal half together.

The proximal half and the distal half each comprise a helical externalthread the external surface of each respective half for engagement withthe two pieces of host material.

The proximal half and the distal half each comprise at least twoopposing self-tapping bores defined through the internal and externalsurfaces and the external threads of each respective half to act as arepository for the removed debris of the host material.

The external threads on the proximal half are arranged and configured inthe opposite helical sense to that of the external threads on the distalhalf.

The threading for threadably engaging the distal half and proximal halftogether comprise: a peg comprising a male threaded portion disposed ona distal end of the proximal half; and a female threaded portion definedon the internal surface of the distal half.

The proximal half and the distal half both comprise a hexagonally shapedinternal bore defined in at least a portion of each respective half.

The apparatus distal half further comprises at least two opposing wrenchflats defined on the external surface.

The external threads on the proximal half are orientated at a differentpitch to that of the external threads on the distal half.

The external threads that have the at least two self-tapping boresdefined therethrough comprise sharp, angled open faces to cut into thehost material when the proximal half and distal half are rotated.

The illustrated embodiment of the invention also includes a method forcoupling at least two pieces of host material together, such as twophlanges of a hammer toe, with an adjustable device comprising the stepsof: inserting a proximal half of the device into a proximal one of thetwo pieces of the host material; inserting a distal half of the deviceinto a distal one of the two pieces of the host material; and couplingthe proximal one of the two pieces of the host material to the distalone of the two pieces of the host material by means of the proximal halfof the device.

The step of inserting the proximal half of the device in the proximalone of the two pieces of the host material comprises the steps of:rotating the proximal half of the device into a predrilled bore; cuttinga female thread into the predrilled bore in the host material by meansof an external thread disposed around the proximal half of the device;and engaging the female thread cut into the host material by means ofthe external thread disposed around the proximal half of the device.

The step of inserting the distal half of the device in the distal one ofthe two pieces of the host material comprises the steps of: rotating thedistal half of the device into a predrilled bore; cutting a femalethread into the predrilled bore in the host material by means of anexternal thread disposed around the distal half of the device; andengaging the female thread cut into the host material by means of theexternal thread disposed around the distal half of the device.

The method further comprises the steps of collecting any debris from thehost material in a repository defined into each of the proximal anddistal halves of the device when each respective device half is beinginserted into its respective one of the two pieces of the host material.

The step of coupling the proximal portion of the host material to thedistal one of the two pieces of the host material by means of theproximal half of the device and the distal half of the device insertedinto each respective one of the two pieces of the host materialcomprises the steps of: disposing or sliding the distal half of thedevice over a male peg disposed on the distal end of the proximal halfof the device; rotating the distal half of the device about the male pegdisposed on the distal end of the proximal half of the device; andengaging a female threaded portion defined in an interior surface of thedistal half of the device to a male thread portion disposed on the malepeg of the proximal half of the device.

The step of rotating the distal half of the device about the male pegdisposed on the distal end of the proximal half of the device comprisesthe steps of: inserting a hex shaped driving tool into a distal end ofthe distal half of the device; engaging the hex shaped driving tool in ahexagonally shaped interior bore of the distal half of the device; androtating the hex shaped driving tool.

The method further comprises the step of adjusting the distance betweenthe proximal one of the two pieces of the host material and the distalone of the two pieces of the host material by means of rotating thedistal and proximal halves of the device after they have been joinedtogether.

The step of rotating the distal half of the device comprises the stepsof: inserting a hex shaped driving tool into a distal end of the distalhalf of the device; engaging the hex shaped driving tool in ahexagonally shaped interior bore of the distal half of the device; androtating the hex shaped driving tool.

The illustrated embodiment of the invention still further includes amethod for coupling at least two pieces of host material together, suchas adjacent phlanges of a hammer toe, with an adjustable devicecomprising the steps of: inserting a proximal half of the device into aproximal one of the two pieces of the host material; inserting a distalhalf of the device into a distal one of the two pieces of the hostmaterial; coupling the proximal one of the two pieces of the hostmaterial to the distal one of the two pieces of the host material bymeans of the proximal half of the device and the distal half of thedevice which has been inserted into each respective one of the twopieces of the host material; collecting any debris from the hostmaterial in a repository defined into each of the proximal and distalhalves of the device when each respective device half is being insertedinto its respective one of the two pieces of the host material; andadjusting the distance between the proximal one of the two pieces of thehost material and the distal one of the two pieces of the host materialby means of rotating the distal half of the device after it has beenjointed to the proximal half of the device.

The step of inserting the proximal half of the device in the proximalone to the two pieces of the host material and inserting the distal halfof the device in the distal one to the two pieces of the host materialcomprises the steps of: rotating each of the proximal and distal halvesof the device; cutting a female thread into each respective one to thetwo pieces of the host material by means of an external thread disposedaround each of the proximal and distal halves of the device; andengaging the female thread in the host material by means of the externalthread disposed around each of the proximal and distal halves of thedevice.

The step of rotating of each of the proximal and distal halves of thedevice comprises the steps of: inserting a hex shaped driving tool intoeach of the distal ends of the distal and proximal halves of the devicerespectively; engaging each hex shaped driving tool in a hexagonallyshaped interior bore in each of the distal and proximal halves of thedevice respectively; and rotating each hex shaped driving tool.

While the apparatus and method has or will be described for the sake ofgrammatical fluidity with functional explanations, it is to be expresslyunderstood that the claims, unless expressly formulated under 35 USC112, are not to be construed as necessarily limited in any way by theconstruction of “means” or “steps” limitations, but are to be accordedthe full scope of the meaning and equivalents of the definition providedby the claims under the judicial doctrine of equivalents, and in thecase where the claims are expressly formulated under 35 USC 112 are tobe accorded full statutory equivalents under 35 USC 112. The inventioncan be better visualized by turning now to the following drawingswherein like elements are referenced by like numerals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of the threaded device depicting both thedistal and proximal portions of the threaded device.

FIG. 2 is a partially cutaway cross-sectional view of the distal portionof the threaded device shown in FIG. 1.

FIG. 3 is a partially cutaway cross-sectional view of the proximalportion of the threaded device shown in FIG. 1.

FIG. 4 is a side cross-sectional view of a hammer toe in which theillustrated embodiment of the invention is employed.

FIG. 5 is a side cross-sectional view of a hammer toe after the jointhas been opened and guide pins inserted in preparation for drilling of areceiving bore into each of the opposing phlanges into which bores thehalves of the bone pin of the illustrated embodiment will be implanted.

FIG. 6 is a side cross-sectional view of a hammer toe after the bone pinhalves of the illustrated embodiment have been implanted, but beforethey have been joined together.

FIG. 7 is a side cross-sectional view of a hammer toe after the bone pinhalves of the illustrated embodiment have joined together.

The invention and its various embodiments can now be better understoodby turning to the following detailed description of the preferredembodiments which are presented as illustrated examples of the inventiondefined in the claims. It is expressly understood that the invention asdefined by the claims may be broader than the illustrated embodimentsdescribed below.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to FIG. 1, a distal half 1 and a proximal half 5 of the bonepin 34 are shown. As described below distal half 1 is implanted in thedistal phlange and proximal half 5 is implanted into the proximalphlange of a hammer toe joint. Both halves 1, 5 are generallycylindrical with a longitudinal bore define therethrough on thelongitudinal axis of each half. The distal half 1 includes an externalhelical thread 3 defined into the exterior surface of the distal half 1.The tooth 32 of the external helical thread 3 is defined between a minordiameter 8 and a major diameter 7. Similarly, an external helical thread4 is also defined into the exterior surface of the proximal half 5,however the external thread 3 of the distal half 1 has a greater pitchthan that of the threads 4 of the proximal half 5. The proximal half 5further comprises a male peg 29 on its distal end. An external helicalthread 6 is defined into the exterior surface of the male peg 29. Amating internal female thread 10 is defined into a bore 11 of theproximal end of the distal half 1.

Both the distal and proximal halves 1, 5 include at least a pair ofdiametrically opposed tapping bores 30 perpendicularly defined throughthe cylindrical surface and perpendicular to the longitudinal axis ofeach half. The tapping bores 30 are preferably oval shaped and aredefined on opposing sides through the threads 3, 4 of each of the halves1, 5 respectively, however other shapes or other configurations may beused without departing from the original spirit and scope of theinvention. The tapping bores 30 are defined with very sharp cuttingedges through the thread 3, 4 to enable the threads 3, 4 to becomeself-tapping. The perpendicular bores 30 also serve as a repository forthe bone chips created during the thread cutting process. This allowsthe chips to be moved into and contained within the perpendicular bore30 in each half 1, 5 thereby preventing galling, interference and radialforces during the thread cutting process. This produces clean cutthreads within the friable bone or other host material similar to thosecut with a tap, but unlike the imperfect threads cut by the crude anddull edges of prior art self-tapping devices.

The internal components of the distal half 1 of the current device canbeen seen in the partially cutaway cross-sectional view of FIG. 2. Thedistal half 1 has an internal bore 11 with a smooth portion forreceiving peg 29 and followed by a threaded portion carrying matingthreads 10, which bore 11 extends from the proximal end 24 of the distalhalf 1 to an internal hexagonally shaped bore 12. Internal female quicklock thread 10 is defined within a portion of the smooth internalsurface 11. The internal hexagonally shaped bore 12 is disposed alongthe longitudinal axis of the distal half 1 and extends to distal end 23of the distal half 1.

Also seen in FIG. 2 is the orientation of the external threads 3 inrelation to the longitudinal axis of the distal half 1. Those externalthreads 3 located proximally of the tapping bores 30 are leading toothflanks 13, and those external threads 3 through which tapping bores 30are defined are trailing tooth flanks 14. The leading tooth flanks 13are orientated at less than a 90 degree angle from the longitudinal axisof the distal half 1. The trailing tooth flanks 14 are orientated at anangle between 90 and 95 degrees relative to the longitudinal axis of thedistal half 1. The recited angles of the leading and trailing toothflanks 13, 14, when engaged in a host material or bone, help produce aninterlocking mechanical grip on the host material or bone. The trailingtooth flanks 14, unlike the leading tooth flanks 13, are open faced dueto the oval shaped tapping bores 30 being defined through them. Thisconfiguration results in the trailing tooth flanks 14 having a sharp,angled edge, which when rotated about the longitudinal axis will cutinto the surrounding bone or host material and thus render bone pin 34self-tapping.

The corresponding internal components of the proximal half 5 of thecurrent device can be seen in FIG. 3. The proximal half 5 includes asmooth, hexagonally shaped internal bore 19 which extends from theproximal end 26 of the proximal half 5, to the distal end 25 of theproximal half 5. The external threads 4 helically disposed around theproximal half 5 have a major diameter 22 and a minor diameter 21. Thoseexternal threads 4 located distally with respect to the tapping bores 30are leading tooth flanks 17, and those external threads 4 through whichthe tapping bores 30 are defined are trailing tooth flanks 18. Theleading tooth flanks 17 are orientated at an angle 90 to 95 degreesrelative to the longitudinal axis of the proximal half 5. The trailingtooth flanks 18 are orientated at an angle less than 90 degrees relativeto the longitudinal axis of the proximal half 5. The recited angles ofthe leading and trailing tooth flanks 17, 18, when engaged in a hostmaterial or bone, help produce an interlocking mechanical grip on thehost material or bone. The cutting faces of the thread teeth are openfaced due to the oval shaped tapping bores 30 defined through them. Thisconfiguration results in the teeth faces having sharp, angled edgeswhich when rotated about the longitudinal axis will cut into thesurrounding bone or host material and thus enable the bone pin 34 to beself-tapping.

Currently, well established medical procedures teach that solid fixationof the toe joint to eliminate articulation is the most satisfactorysolution for treating the common malady of hammer toe. The currentdevice helps accomplish this procedure in a novel and improved way bybeing inserted between the proximal and distal phalanges of a patient.

First, a surgeon or other medical professional opens the soft tissues ofthe patient's hammer toe as shown in FIG. 4 and then surgicallypartially separates the joint. The joint is then opened furthered bybending the partially disconnected distal phalanges downward to exposethe proximal end of the bone as shown in cross-sectional view of FIG. 5.A guide pin hole is then drilled through the end of the proximal portionof the bone and then a guide pin 36 is then installed to help facilitatethe use of a cannulated drill bit to further open the inside of the boneinto a large enough cavity to accommodate the proximal half 5 of thebone pin 34.

The proximal end 26 of the proximal half 5 is inserted into the drilledhole in the proximal phlange. A hex shaped driving tool, commonly knownin the art, is then inserted into the distal end 25 of the proximal half5 and extended into the hexagonally shaped internal bore 19. Theproximal half 5 is then screwed into the surrounding bone in theproximal phlange by rotating the hex shaped driving tool. As theproximal half 5 is being rotated, the open faced trailing tooth flanks18 cut into the surface of the surrounding bone of the proximal phlangeand allow the external threads 4 to dig deeper into the bone. Bone chipsor any other refuse from the host material is removed by the externalthreads 4 and pushed into the oval shaped tapping bores 30 and out ofthe way of the self-tapping external threads 4, thus preventing gallingand any unnecessary radial forces from being produced. As the proximalhalf 5 is rotated into the bone, the external threads 4 self-tap theproximal half 5 more deeply into the proximal phlange and more securelyimplant half 5 into the host material, until just the male peg 29 isleft protruding beyond the end of the proximal phlange.

With the distal phalanges bent downward a second pilot hole is drilledinto the proximal end of the bone of the distal phalanges entirelythrough to the distal end of the toe. An alignment pin is inserted intothe pilot hole in the proximal end of the distal bone at the openedjoint. The cannulated drill is inserted over the pin and used toincrease the size of the pilot hole to a depth to allow insertion of thedistal half 1 of the bone pin 34.

The distal end 23 of the distal half 1 is first inserted into theproximal end of the distal phlange and a hex shaped driving tool,commonly known in the art, is inserted into the proximal end 24 of thedistal half 1. In order to be inserted correctly, the hex shaped drivingtool extends past the internal female quick lock thread 10 and into theinternal hexagonally shaped bore 12. Once the hex driving tool is inplace, the distal half 3 is then rotated into the pilot hole in the samefashion as the proximal half 5. As the distal half 1 is being rotated,the open faced trailing tooth flanks 14 cut into the surface of thesurrounding bone and allow the external threads 3 to dig deeper into thebone of the distal phlange. Bone chips or any other refuse from the hostmaterial is removed by the external threads 3 and pushed into the ovalshaped tapping bores 30 and out of the way of the self-tapping externalthreads 3, thus preventing galling and any unnecessary radial forcesfrom being produced. As the distal half 1 is rotated into the bone, theexternal threads 3 self-tap the distal half 1 more deeply into the boneand half 1 is more securely implanted into the bone, until just a fillet27 defined on the proximal end 24 of the distal half 1 is leftprotruding beyond the proximal end of the bone of the distal phlange.

Holding the proximal phalange that contains the proximal half 5 in onehand, the surgeon pulls distal phalange containing the distal half 1away slightly while rotating the distal phlange counterclockwise so thatthe proximal end 24 of the distal half 1 is installed over the distalend 25 of the proximal half 5, making sure that the male peg 29 isaligned with and inserted into the smooth inner bore 11 of the distalhalf 1. The distal half 1 may then be tightened and coupled to theproximal half 5 by either using a spanner wrench commonly known in theart interfaced with two opposing wrench flats 16 defined on the externalsurface of the distal half 1 as shown in FIG. 1, or by using a hexshaped wrench inserted through the drilled pilot hole at the distal endof the toe and into the distal end 23 of the distal half 1. In thelatter instance the hex wrench is inserted into the internal hexagonallyshaped bore 12 and then rotated. As the distal half 1 is being rotated,the external threads 6 on the male peg 29 of the proximal half 5 engagethe internal female quick lock thread 10. The distal half 1 is rotatedabout the male peg 29 until the male peg 29 makes contact with theshoulder 36 at the proximal end of internal hexagonal bore 12 andfurther engagement with the internal female quick lock thread 10 is nolonger possible. With the distal half 1 and proximal half 5 now firmlycoupled together, the bone pin 34 comprised of halves 1 and 5effectively becomes a single piece. The bone pin 34 is further rotatedby the hex wrench in a clockwise direction, which due to the opposingleft and right hand orientated threads of the distal half 1 and proximalhalf 5 as discussed above, cause the separated proximal and distalphalanges to be drawn together and further increase the stability andstrength of the coupling of the bone pin 34. The distance between thephalanges can then be easily adjusted by rotation of the coupledproximal half 5 and distal half 1 in either a clockwise orcounterclockwise direction as shown in FIG. 7.

Many alterations and modifications may be made by those having ordinaryskill in the art without departing from the spirit and scope of theinvention. Therefore, it must be understood that the illustratedembodiment has been set forth only for the purposes of example and thatit should not be taken as limiting the invention as defined by thefollowing invention and its various embodiments.

Therefore, it must be understood that the illustrated embodiment hasbeen set forth only for the purposes of example and that it should notbe taken as limiting the invention as defined by the following claims.For example, notwithstanding the fact that the elements of a claim areset forth below in a certain combination, it must be expresslyunderstood that the invention includes other combinations of fewer, moreor different elements, which are disclosed in above even when notinitially claimed in such combinations. A teaching that two elements arecombined in a claimed combination is further to be understood as alsoallowing for a claimed combination in which the two elements are notcombined with each other, but may be used alone or combined in othercombinations. The excision of any disclosed element of the invention isexplicitly contemplated as within the scope of the invention.

The words used in this specification to describe the invention and itsvarious embodiments are to be understood not only in the sense of theircommonly defined meanings, but to include by special definition in thisspecification structure, material or acts beyond the scope of thecommonly defined meanings. Thus if an element can be understood in thecontext of this specification as including more than one meaning, thenits use in a claim must be understood as being generic to all possiblemeanings supported by the specification and by the word itself.

The definitions of the words or elements of the following claims are,therefore, defined in this specification to include not only thecombination of elements which are literally set forth, but allequivalent structure, material or acts for performing substantially thesame function in substantially the same way to obtain substantially thesame result. In this sense it is therefore contemplated that anequivalent substitution of two or more elements may be made for any oneof the elements in the claims below or that a single element may besubstituted for two or more elements in a claim. Although elements maybe described above as acting in certain combinations and even initiallyclaimed as such, it is to be expressly understood that one or moreelements from a claimed combination can in some cases be excised fromthe combination and that the claimed combination may be directed to asubcombination or variation of a subcombination.

Insubstantial changes from the claimed subject matter as viewed by aperson with ordinary skill in the art, now known or later devised, areexpressly contemplated as being equivalently within the scope of theclaims. Therefore, obvious substitutions now or later known to one withordinary skill in the art are defined to be within the scope of thedefined elements.

The claims are thus to be understood to include what is specificallyillustrated and described above, what is conceptionally equivalent, whatcan be obviously substituted and also what essentially incorporates theessential idea of the invention.

We claim:
 1. An apparatus for coupling two pieces of host materialtogether, comprising: a distal half and a proximal half, each said halfhaving a longitudinal axis which, when conjoined, couple respectively afirst piece of host material to a second piece of host material along anow common longitudinal axis, said distal half having a thread patternhelically disposed on an exterior surface, wound in one direction, saidproximal half having a thread pattern helically disposed on an exteriorsurface wound in a second direction, opposite from said distal half,means to removeably attach said distal and proximal halves together suchthat when united together, further rotation of either said proximal ordistal half causes said halves to move one relative to the other untilthey are either dissociated or bound together, wherein said threads onsaid exterior surfaces each have a portion defining self-tapping threadslocated adjacent bores which pass through said exterior surfaces intointeriors thereof, said self-tapping threads having tooth flanks on eachhalf facing each other and defining an included angle relative to saidlongitudinal axes of said proximal and distal halves of less than 90degrees, and each thread of said self-tapping threads has an oppositeflank on each tooth with an included angle relative to said longitudinalaxes of said proximal and distal halves greater than or equal to 90degrees, wherein said means to removeably attach said distal andproximal halves together includes a peg projecting axially from saiddistal half and having a thread disposed at a terminus for threadedaxial registry with a complementary formed thread disposed in saidproximal half, wherein said means to removeably attach said halvesfurther includes wrench flats disposed on an exterior surface of saidpeg.
 2. The apparatus of claim 1 wherein said means to removeably attachsaid halves further includes a hexagonal bore formed in said halves. 3.The apparatus of claim 1 wherein said thread pattern on said distal halfhas a pitch different than that of said thread pattern on said proximalhalf.